1. Field of the Invention
The present invention relates to medical devices and methods. More specifically, the invention relates to intervertebral spacers methods for dynamically promoting bone growth and fusion following implantation of the spacer.
Back pain takes an enormous toll on the health and productivity of people around the world. According to the American Academy of Orthopedic Surgeons, approximately 80 percent of Americans will experience back pain at some time in their life. In the year 2000, approximately 26 million visits were made to physicians' offices due to back problems in the United States. On any one day, it is estimated that 5% of the working population in America is disabled by back pain.
Common causes of back pain are injury, degeneration and/or dysfunction of one or more intervertebral discs. Intervertebral discs are the soft tissue structures located between each of the thirty-three vertebral bones that make up the vertebral (spinal) column. Essentially, the discs allow the vertebrae to move relative to one another. The vertebral column and discs are vital anatomical structures, in that they form a central axis that supports the head and torso, allow for movement of the back, and protect the spinal cord, which passes through the vertebrae in proximity to the discs.
When a damaged intervertebral disc causes a patient pain and discomfort, surgery is often required. Typically, surgical procedures for treating intervertebral discs involve discectomy (partial or total removal of a disc), often followed by interbody fusion of the superior and inferior vertebrae adjacent to the disc. Fusion is most commonly achieved by implantation of a cage or spacer together with bone graft material to promote bone growth to fuse the adjacent vertebrae together. Oftentimes, pins, rods, screws, cages and/or the like are placed between the vertebrae to act as support structures to hold the vertebrae and bone graft material in place while the bones permanently fuse together.
While such fusion procedures have been very successful for many patients, it some cases the fusion spacers or cages can be difficult to implant, and the bone regrowth necessary to achieve complete fusion can take an excessive period of time. Therefore, a need exists for improved spacers and methods for fusing the spacers to promote complete and rapid bone regrowth. At least some of these objectives will be met by the inventions described herein below.
2. Description of the Background Art
A compliant block intended to be implanted between adjacent vertebrae to promote fusion as described in U.S. Pat. No. 6,395,033. Partially compliant fusion cages and spacers are described in U.S. Pat. No. 8,685,101 and U.S. Pat. Publ. 2009-0093885. An interspinous fusion device which dynamically promotes bone growth is described in U.S. Pat. Publ. 2013-0296940. Flexible devices which may be coiled and implanted between vertebrae are described in U.S. Pat. Nos. 7,666,226 and 7,947,078. A bone implant that may have a U-shape is described in U.S. Pat. No. 6,652,592.